arXiv subjects

Soham Sen

Publications and source records attributed to Soham Sen.

At least 19 recordsLinked to original sources

arXiv2026

Towards graviton lasing from squeezed ultra-cold systems

In our recent work, arXiv:2604.11474 [hep-th], we have shown that effective detection of gravitons is possible using an array of charged harmonic oscillators in a dynamical electromagnetic field. Using the interaction Hamiltonian of the identical model, we find out that a systematic way of population inversion of the gravitons is possible in ultra-cold atomic systems. We find out that the exponential growth depends strictly on the number of bosons in the system as well as their inherent squeezing of the matter wave packets. A coherent source of gravitons may lead directly to an unavoidable evidence on the existence of gravitons and based on this analysis we propose an experimental proposal for generating true graviton laser.

hep-th↗

arXiv2026

Post-Newtonian analysis of the quantum signatures of gravity

In a recent work \href{https://doi.org/10.1103/PRXQuantum.2.010325}{PRX QUANTUM 2 (2021) 010325}, a new way of investigating quantum gravity signatures using quantum information theoretic techniques, have been proposed. The primary result of this analysis revealed that non-Gaussianity can arise only through the consideration of a quantum model for the gravity part. Compared to classical gravity, only quantum gravity can result in non-quadratic operators in the Hamiltonian which leads to the non-Gaussian behavior. In our current analysis, we have considered a more realistic scenario taking into effect leading order post-Newtonian corrections in the analysis. We have stayed with the same model of a Bose-Einstein condensate placed inside a harmonic trap potential which indeed works as the detector of the non-Gaussianity generated due to quantum gravitational effects. Bose-Einstein condensates are experimentally well studied; apart from being a single quantum system, they include Feshbach resonances, which helps tuning the strength of the electromagnetic interactions which in principle can be set to zero. This is important since it can help distinguish quantum gravity from electromagnetic interactions without affecting gravitational interactions, and any non-Gaussianity can then be solely attributed to quantum gravity. We observe that the signal to noise ratio gets slightly damped due to the post-Newtonian effects taken under consideration.

hep-th↗

arXiv2026

Quantum gravitational deflection of parallel matter wave beams

It is well known that two parallel photon beams do not deflect under the effect of their energy-momentum tensor. In this work, we propose a novel model where two spatially separated Bose-Einstein condensates are outcoupled to create two parallel atom laser beams. We find out that apart from the classical deflection, a purely quantum gravity induced tidal deflection is observed which results in an irreducible noise in the geodesic separation of the two beams. Based on this simple but novel theoretical outcome, we propose an experimental model for detecting this quantum gravity induced standard deviation in the geodesic separation of the two parallel matter-wave beams.

gr-qc↗

arXiv2026

Gravity mediated entanglement of phonons in Bose-Einstein condensates

The eigenstates of two test-masses (where each test-mass is placed inside of a harmonic trap) separated by a distance, can get entangled where gravity acts as the mediator of entanglement and it has been argued in \href{https://doi.org/10.48550/arXiv.2511.07348}{arXiv:2511.07348 [quant-ph]} that this entanglement of masses cannot be generated without the underlying quantum nature of gravity. In this work, we consider two non-relativistic Bose-Einstein condensates (formed inside of harmonic trap potentials with identical trapping frequencies) separated by a distance. We take a linearized quantum gravity model and investigate the generation of entanglement while gravitons serve as the mediator of entanglement. The entanglement is generated between the phonon modes of the two condensates, and we observe that for very low separation distance, the entanglement generated is significantly higher than that observed for the quantum gravity induced entanglement of masses or QGEM protocol; however, the fall of entanglement is faster than the two-particle case for two separated Bose-Einstein condensates. We observe that when the number of particles in the condensate is increased, the degree of entanglement for a smaller separation distance becomes substantially higher compared to the case discussed in \href{https://doi.org/10.1103/PhysRevD.105.106028}{Phys. Rev. D 105 (2022) 106028}, which allows for a more robust experimental proposal using this quantum gravity induced entanglement of phonons or QGEP protocol.

hep-th↗

arXiv2026

Signatures of Quantum Gravity In Relativistic Quantum Systems

In this thesis, we have used a linearized quantum gravity setting to investigate the effects of gravitons on matter systems. Based on the graviton-matter interaction, we have then proposed detector models that may be able to pick up graviton-induced signatures in a matter of a few years. We start with the simple model of a two-particle model detector system interacting with quantized gravitational fluctuations while the detector degrees of freedom obey the generalized uncertainty principle (GUP). For the first part we have hinted at the existence of quantum gravity induced memory effect as well as obtained a quantum gravity modified uncertainty relation. For the next part of the thesis, we have mainly focused on the phenomenological aspects of a linearized quantum gravity theory. For the initial phenomenological model, we have considered the same two-particle model detector system interacting with gravitational fluctuations where the entire set-up is placed inside a harmonic trap potential and looked at the stimulated absorption and spontaneous emission scenario for gravitons. In order to inspect a more involved phenomenological aspect, instead of the standard matter-detector system, we make use of a relativistic scalar Bose-Einstein condensate (BEC) and investigated the response of the BEC based model towards incoming gravitons and proposed a graviton detector based on graviton mediated decoherence from entangled BECs.

gr-qc↗

arXiv2026

`Seeing' the quantum ripples of spacetime

We propose a novel way of detecting gravitons using emission of photons from charged array of quantum harmonic oscillators placed inside of a cavity while the cavity is being pumped with low frequency photons. We observe that when the detector is in its ground state, a single graviton is absorbed by the detector while it jumps a single energy level by simultaneously emitting a photon. We also observe that while the detector de-excites from an higher energy level, it spontaneously emits a high frequency graviton, by absorbing a single photon. This analytical outcome encourages us to propose a very simple tabletop graviton detector model as the transition probabilities can be significantly enhanced by pumping photons in the initial state of the system. This mechanism gives us a physical way to `visualize' the effect of gravitons with a relativistic system. We also show that Dyson's original argument on the non-detectability of gravitons can be completely circumvented using our proposed graviton detector.

hep-th↗

arXiv2026

Detecting gravitational waves by emission of photons from charged Weber bars

In this work, we propose a novel experimental set-up using charged resonant gravitational wave detectors. We exploit the semi-classical analogue of the Gertsenshtein effect where the gravitational wave acts as an modulator for the optomechanical system. We consider a cavity QED scenario where the Weber bar is placed inside an electromagnetically shielded cavity. We observer that when the gravitational wave falls on the Weber bar, it emits photon which signifies the detection of gravitational waves by the resonant bars. The frequency controlled spontaneous emission scenario will shed a new light on future generation of efficient gravitational wave detector models.

gr-qc↗

arXiv2025

Quantum coherence measures in entangled atomic systems

In this study, we investigate the effect of the Lorentz transformation on the measures of quantum coherence in an entangled atomic system. Here, we consider the effect of this relativistic boosts on two-particle entangled generalized Gaussian wave packets in two scenarios. In the first scenario, we consider that the relativistic boost affects the one particle and other remains unaffected while in the second scenario, we consider that both the particles are affected by the effect of the relativistic boost. The coherence of the wave function as measured by the boosted observer is studied as a function of the boost parameter and the width of the Gaussian wave packets. Using various formulations of coherence, it is shown that in general the coherence decays with increase in the width of the Gaussian wave packet, higher values of boost parameter, and the number of particles on which boost is applied.

quant-ph↗

arXiv2025

Governing Automated Strategic Intelligence

Military and economic strategic competitiveness between nation-states will increasingly be defined by the capability and cost of their frontier artificial intelligence models. Among the first areas of geopolitical advantage granted by such systems will be in automating military intelligence. Much discussion has been devoted to AI systems enabling new military modalities, such as lethal autonomous weapons, or making strategic decisions. However, the ability of a country of "CIA analysts in a data-center" to synthesize diverse data at scale, and its implications, have been underexplored. Multimodal foundation models appear on track to automate strategic analysis previously done by humans. They will be able to fuse today's abundant satellite imagery, phone-location traces, social media records, and written documents into a single queryable system. We conduct a preliminary uplift study to empirically evaluate these capabilities, then propose a taxonomy of the kinds of ground truth questions these systems will answer, present a high-level model of the determinants of this system's AI capabilities, and provide recommendations for nation-states to remain strategically competitive within the new paradigm of automated intelligence.

cs.AI↗

arXiv2025

Density matrix analysis of systems influenced by periodic Hamiltonians

In this work, we consider simple systems that are influenced by Hamiltonians with time periodicity. Our analysis is mainly focussed on the density matrix approach and aims to solve the Liouville equation of motion from which one can extract the state of the system when the system is in a pure state. We start our analysis with the standard Rabi-oscillation problem. We consider a density matrix corresponding to the entire model system and solve the Liouville equation of motion. We have then made use of the Lewis-Reisenfeld invariant approach and arrive at the exact same result which implies that the density matrix of the system can indeed be identified with the Lewis invariant. Finally, we consider a two-level system with a constant magnetic field in the $z$-direction and a time dependent magnetic field in the $x$-direction. Finally, we solve the Liouville equation of motion for this system and calculate the various coherence measures and plot them to investigate the time dependence and reliability of different coherence measures.

quant-ph↗

arXiv2025

Derivative coupling in horizon brightened acceleration radiation: a quantum optics approach

Horizon Brightened Acceleration Radiation (HBAR) signifies a unique radiation process and provides a promising framework in exploring acceleration radiation in flat/ curved spacetime. Its construction primarily relies on the transition probability of an atom falling through a high-Q cavity while interacting with a quantum field. The HBAR effect has typically been explored in the context of minimal coupling between the atom and the field amplitude. However, the minimally coupled models are affected by the infrared (IR) divergences that arise in the massless limit of the quantum fields in (1+1) dimensions. Thus, in the present manuscript, we examine the HBAR process using both the point-like and finite size detectors coupled with the momentum of the field, which plays a crucial role in naturally resolving IR divergences. Our results suggest that the transition probability for the point-like detector is independent of its frequency. This can be interpreted as the influence of the local gravitational field which modifies the sensitivity of the detector to its frequency and broadens its effective frequency range. Through a comparative study based on the length of the detector, we find that for a detector with a smaller length, the steady state solution for the density matrix of the field vanishes. This may indicate the existence of a non equilibrium thermodynamic state under the condition of finite size detector-field interaction. These distinctive features are exclusive to the derivative coupling between the atom and the field, highlighting them as a compelling subject for future investigation.

gr-qc↗

arXiv2025

Inverse logarithmic correction in the HBAR entropy of an atom falling into a renormalization group improved charged black hole

In this work, we have considered a spherically symmetric non-rotating charged black hole geometry where both the Newton's gravitational constant and the charge of the black hole flows with the energy scale. We have used the Kretschmann scale identification to write down the finite cutoff for the momentum scale in terms of the proper distance. Introducing the flow of running couplings, the event horizon radius of the black hole using quantum improved Reissner-Nordstrom metric was found in \href{https://doi.org/10.1103/PhysRevD.104.066016}{Phys. Rev. D 104 (2021) 066016}. We have, in this work, explored the thought experiment of a two-level atom freely falling into the event horizon of a quantum improved charged black hole and have computed the transition probability of the atom for going from its ground state to the excited state via emission of a virtual photon. We find that the probability deviates slightly from the pure Planckian spectrum. We have showed that this deviation is due to the presence of incomplete lower gamma function in the distribution function. We have then computed the horizon brightened acceleration radiation entropy and found that it is identical to the Bekenstein-Hawking entropy followed by the renormalization group correction terms including an inverse logarithmic and a square root of the area term due to emitting photons.

gr-qc↗

arXiv2024

Renormalization group improved cosmology in the presence of a stiff matter era

In \href{https://link.aps.org/doi/10.1103/PhysRevD.92.103004}{Phys. Rev. D 92 (2015) 103004}, simple analytical solutions of the Friedman equations were obtained for a universe having stiff matter component in the early universe together with a dark matter, and a dark energy component. In this analysis, the universe is considered to be made of a dark fluid which behaves as a stiff matter in the early phase of the universe (when the internal energy dominates). It is also more logical to consider quantum gravitational effects in the early phase of the cosmological evolution. In this analysis, following \href{https://link.aps.org/doi/10.1103/PhysRevD.65.043508}{Phys. Rev. D 65 (2002) 043508}, we consider renormalization group improved modified Friedmann equations where the Newton's gravitational constant (G) and the cosmological constant (\Lambda) flows with the momentum scale of the universe. It is observed that for a universe undergoing a stiff matter era, radiation era, and matter era, inflation is absent in the early time regime of the universe when the flow of the Newton's gravitational constant and cosmological constant is under consideration. Using the identification of the momentum scale with the scale factor of the universe, we then explore the era $t>t_{\text{Pl}}$ which indicates a primarily matter dominated era with accelerated expansion due to the presence of dark energy. Finally, considering the total equation of state as a combination of linear equation of state along with a polytropic equation of state, we observe that after the Planck-time the universe can undergo an inflationary phase and we find out that the inflation is enhanced by quantum gravitational effects arising due to the consideration of renormalization group approach to quantum gravity

gr-qc↗

arXiv2024

Quantum nature of gravity in a Bose-Einstein condensate

The effect of noise induced by gravitons on a Bose-Einstein condensate has been explored in (Phys. Rev. D 110 (2024) 026014; https://link.aps.org/doi/10.1103/PhysRevD.110.026014). In the previous paper, we investigated the effects of graviton while detecting a gravitational wave using a Bose-Einstein condensate. In this work we shall explicitly calculate the decoherence due to the noise of gravitons between two momentum states of the Bose-Einstein condensate. This decoherence happens due to Bremsstrahlung from the Bose-Einstein condensates due to the effect of the noise induced by gravitons. It is also observed that the two states become entangled because of the existence of a surrounding graviton field which degrades over time via means of this gravitational Bremsstrahlung. Using this property of the Bose-Einstein condensate in a quantum gravity background, we propose an experimental test via the use of atom lasers (generated from the condensate) which would, in principle, help to detect gravitons in future generations of very advanced ultra-cold temperature experiments.

hep-th↗

arXiv2024

Thermodynamics of a Schwarzschild black hole surrounded by quintessence in the generalized uncertainty principle framework

We investigate the thermodynamics of a Schwarzschild black hole, surrounded by the quintessence energy-matter in the linear and quadratic generalized uncertainty principle framework. Considering the variance in the position to be of the order of the event horizon radius and equating the variance in the momentum to the Hawking temperature of the black hole, we substitute these variances in the deformed algebra. From there we obtained the generalized uncertainty principle-modified black hole temperature and eventually the specific heat of the black hole. Then we calculate the critical as well as the remnant mass and obtain the entropy relation. We observe that the entropy relation includes the usual leading order ``\textit{area divided by four}" term, sub-leading logarithmic term, and higher order inverse of the area corrections. Finally, calculating the energy output as a function of time, we obtain the evaporation time of the black hole. The results show the dependence of the quintessence parameter on the thermodynamic quantities in the framework of linear and quadratic generalized uncertainty principle.

gr-qc↗

arXiv2024

Quantum coherence measures for generalized Gaussian wave packets under a Lorentz boost

In this paper we consider a single particle, spin-momentum entangled state and measure the effect of relativistic boost on quantum coherence. The effect of the relativistic boost on single-particle generalized Gaussian wave packets is studied. The coherence of the wave function as measured by the boosted observer is studied as a function of the momentum and the boost parameter. Using various formulations of coherence, it is shown that in general the coherence decays with the increase in momentum of the state, as well as the boost applied to it. A more prominent loss of coherence due to relativistic boost is observed for a single particle electron than that of a neutron. The analysis is carried out with generalized Gaussian wave packet of the form $\mathcal{N} p^n \exp(-\frac{p^2}{\sigma^2})$ with $n$ being the ``generalization parameter" and $\mathcal{N}$ denoting the appropriate normalization constant. We also obtain a range for parameter $n$ appearing in the wave packet. The upper bound is found to have a dependence on the mass of the particle and the width of the Gaussian wave packet. We have obtained the Frobenius-norm measure of coherence, $l_1$ and $l_2$ norm measure of coherence, and relative entropy of coherence for a (1+1) and (3+1)-dimensional analysis. Corresponding to each of the cases, we observe that the $l_1$ norm measure of coherence is equal to the Frobenius norm measure of coherence. We have analyzed the scenario for which such a beautiful coincidence can occur. Finally, we have plotted different measures of coherence for the electron as well as the neutron for different values of the width of the wave-function $\sigma$, boost parameter $\beta$, and generalization parameter $n$.

quant-ph↗

arXiv2024

Quantum gravity signatures in gravitational wave detectors placed inside a harmonic trap potential

In this work, we consider a general gravitational wave detector of gravitational wave interacting with an incoming gravitational wave carrying plus polarization only placed inside a harmonic trap. This model can be well acquainted with the description of a resonant detector of gravitational wave as well. The well known detector-gravitational wave interaction scenario uses the method of a semi classical approach where the detector is treated quantum mechanically but the gravitational wave is considered at a classical level. In our analysis, we use a discrete mode decomposition of the gravitational wave perturbation which results in a Hamiltonian involving the position and momentum operators corresponding to the gravitational wave and the harmonic oscillator. We have then calculated the transition probability for the harmonic oscillator-gravitational wave tensor product state for going from an initial state to some unknown final state. Using the energy flux relation of the gravitational waves, we observe that if we consider the total energy as a combination of the number of gravitons in the initial state of the detector then the transition probability for the resonant absorption case scenario takes the analytical form which is exactly similar to the semi-classical absorption case. In case of the emission scenario, we observe a spontaneous emission of a single graviton which was completely absent in the semi-classical analouge of this model. This therefore gives a direct signature of linearized quantum gravity.

hep-th↗

arXiv2024

Atom falling into a quantum corrected charged black hole and HBAR entropy

In an earlier analysis \href{https://link.aps.org/doi/10.1103/PhysRevD.105.085007}{Phys. Rev. D 105 (2022) 085007}, we have explored the event of acceleration radiation for an atom freely falling into the event horizon of a quantum-corrected Schwarzschild black hole. We want to explore the acceleration-radiation when the atom is freely falling into the event horizon of a charged quantum-corrected black hole. We consider the quantum effects of the electromagnetic field along with the gravitational field in an asymptotic safety regime. Introducing the quantum improved Reisner-Nordstr\"{o}m metric, we have calculated the excitation probability of a two-level atom freely falling into the event horizon of quantum improved charged black hole. Recently, in the case of the braneworld black hole (where the tidal charge has the same dimension as the square of the charge of a Reissner-Nordstr\"{o}m black hole in natural units), we have observed from the form of the transition probability that the temperature will have no contribution in the first order of the tidal charge. We observe that for a quantum corrected Reissner-Nordstr\"{o}m black hole, there is a second-order contribution in the charge parameter in the temperature that can be read off from the transition probability. Next, we calculate the HBAR entropy in this thought experiment and show that this entropy has a leading order Bekenstein-Hawking entropy term along with some higher order correction terms involving logarithmic as well as fractional terms of the black hole area due to infalling photons. We have finally investigated the validity of Wien's displacement law and compared the critical value of the field wavelength with the general Schwarzschild black hole and its corresponding quantum-corrected case.

gr-qc↗